OT: "An Alternator is a Battery Maintainer, -NOT a Battery Charger."

[BRENT in 10-uh-C]

This comment in the title was recently told to me by a battery salesman. I have thought and thought about this, -and even looked online where I have read the same comment multiple times.

So help me understand what I don't understand about (t)his comment. So if a battery in a Model-A is at 100% capacity ( i.e.: fully charged ), and the engine starts after a prolonged cranking, let's hypothetically say that the battery is now at 90% capacity ( -or 90% of fully-charged ). If an alternator is only a 'maintainer', then is it reasonable to assume that the best that can be expected is the battery will remain at 90%? Then the next time the engine is started, the battery charge may drop to 85%, ...and so on until the voltage has dropped to a point the battery cannot turn the starter motor.

So if the point about an alternator is only a maintainer and not a charger, how is it that a battery can go so long without needing to be placed on a dedicated 'battery charger' to return it to 100%??

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